In the refining of petroleum or manufacture of fuels from fossil materials or various sources of hydrocarbonaceous sources, an olefinic mixture is often produced. For instance, in cracking heavier petroleum fractions, such as gas oil, to make gasoline or distillate range products, light gases containing ethene, propene, butene and related aliphatic hydrocarbons are produced. It is known to recover these valuable dry-products for use as chemical feedstocks for other processes, such as alkylation, polymerization, oligomerization, LPG fuel, etc. Ethylene is particularly valuable as a basic material in the manufacture of polyethylene and other plastics, and its commercial value is substantially higher as a precursor for the chemical industry than as a fuel component. Accordingly, it is desirable to separate ethylene in high purity for such uses.
A typical byproduct of fluid catalytic cracking (FCC) units is an olefinic stream rich in C.sub.2 -C.sub.4 olefins, usually in mixture with lower alkanes. Ethylene can be recovered from such streams by conventional fractionation means, such as cryogenic distillation, to recover the C.sub.2 and C.sub.3.sup.+ fractions; however, the equipment and processing costs are high. It is an object of the present invention to provide a novel process and apparatus for separating ethylene from olefinic mixtures economically.